This invention relates to a printer or typewriter, and more particularly to a printer or typewriter in which a ribbon supply is mounted on a stationary section of the machine and a print ribbon is passed through a print head on a carrier and is fed in relation to movement of the carrier.
In a printer or typewriter of the type described, and especially in a thermal printer or typewriter which has a thermal print head on a carrier, a print ribbon such as a ribbon having thermally transferrable ink thereon is fed an extent corresponding to a distance of and in a direction opposite to the direction of translatory movement of the carriage as the carriage advances to print a line of characters on a medium supported on a platen, or in other words, a print ribbon is fed in such a manner as to provide no relative movement between the medium and the print ribbon. If otherwise there is some relative movement between them, then ink once transferred to the medium will be diffused over the medium due to such relative movement and will blur the medium, resulting in poor print. A print ribbon feeding mechanism which attains such a print ribbon feeding manner as described just above is disclosed in a U.S. Pat. No. 3,855,448 and especially by an embodiment of FIG. 5 of the patent. This mechanism includes a clamp provided at a stationary section of the machine for clamping a used portion of a print ribbon while a print head is advancing, and a one-way roller provided on the carrier which allows the print ribbon to pass the same when the carrier advances but prevents the ribbon from passing in the opposite direction so that it draws out the ribbon from a supply reel when the carrier is returned to its leftmost end position while the ribbon is wound onto a takeup reel correspondingly. This arrangement, however, is somewhat disadvantageous in that a print ribbon is "fed" wastefully even when a carriage advances without printing any character, that is, without using the print ribbon, such as in a spacing or tabbing operation, since the print ribbon is fed an extent equal to a distance over which the carrier advances. Further, if a takeup reel is not appropriately driven to takeup a print ribbon in timed relationship with returning movement of the carrier in any position of the reel, then the ribbon may be either pulled so heavily to break or slackened between the takeup reel and the one-way roller to cause jamming. The patent, however, does not disclose any solution to this problem.